Drop-on-demand ink jet printers use thermal energy to produce a vapor bubble in an ink-filled chamber to expel an ink droplet. A thermal energy generator or heating element, usually a resistor, is located in the chamber on a heater chip near a discharge orifice or nozzle. A plurality of chambers, each provided with a single heating element, are provided in the printer's printhead. The printhead typicadly comprises the heater chip and a plate having a plurality of the discharge orifices formed therein. The printhead forms part of an ink jet print cartridge which also comprises an ink-filled container.
The print cartridge container includes one or more ink chambers. For a monochrome or single color print cartridge, one chamber is provided. For a three color print cartridge, three chambers are included. The print cartridge container may also include a filter/standpipe assembly for each chamber. The standpipe defines a passageway through which ink flows as it travels from the chamber to the printhead. The filter is attached to the standpipe and functions to remove air bubbles and contaminants from the ink before the ink reaches the printhead. Contaminants, if not removed from the ink, may block orifices in the printhead orifice plate, thereby preventing ink from being ejected from those orifices.
The quality of printed images produced by an ink jet printer depends to a large degree on the resolution of the printer. Higher or finer resolution wherein the dots are more closely spaced provides for higher quality images.
A consideration with increasing the resolution of ink jet printers is that increased resolution results in more printed dots per unit area. For example, doubling print resolution from 600.times.600 dpi to 1200.times.1200 dpi results in four times as many dots per unit area. Since the number of dots per unit area increases with increased resolution, the size of each printed dot must decrease in order to avoid saturating the print media. Hence, the size of the orifices in the orifice plate must decrease. In order to prevent the smaller orifices from becoming blocked or obstructed by contaminants contained in ink, finer filters are required.
Conventional filters attached to standpipes are typically made from a metal mesh. It is believed that very fine metal mesh filters would be costly to produce. Further, it is believed that ink pressure drop across a very fine metal mesh filter would be large due to the meandering flow path the ink must take as it passes through the metal mesh.
U.S. Pat. Nos. 5,124,717, 5,141,596 and 5,204,690 teach providing filters in silicon channel plates. In these printhead devices, two separate silicon substrates are required, one for the heater chip and one for the channel plate. Because silicon is an expensive material, these printhead devices are believed to be impractical.
Accordingly, there is a need for an improved low cost filter which is capable of removing particles of varying sizes including very small particles from ink without also effecting a large drop in fluid pressure across the filter.